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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Datasheets and probability
Date: Sun, 15 Dec 2024 17:33:05 +1100
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On 15/12/2024 12:50 pm, John S wrote:
> Hi, men -
> 
> There are sometimes 3 columns on a datasheet which may contain min, nom, 
> and max values. Like Vds for example.
> 
> Is there any probability tacitly assigned to the values? I know that 
> nominal is the average, and I assume that the value lies between the two 
> middle one standard deviation points.
> 
> 1. Is that a valid assumption?
> 
> 2. Is the min between one and two standard deviations down from the mean?
> 
> Thanks and I apologize for asking such a basic question in this 
> professional group.

I doubt very much that this hasever been spelled out, but a span of two 
standard deviations above and below the mean would include 95% of a 
randomly distributed variable, which would mean that one customer in 
twenty might complain about getting an out-of-spec component.

I haven't done it that often, which suggests that the industry has a 
adopted a three standard deviation span which would include 99.5% of a 
randomly distributed variable.

I have bitched about duff components enough to fit that, but most of 
them were fine at room temperature and only fell out of spec after 
they'd warmed up, or to be more precise, after they'd been stuck in a 
box in an enclosed rack and had had time to warm up a bit.

-- 
Bill Sloman, Sydney